The IN BACKGROUND TASK statement allows you to execute remote enabled function modules in a background task asynchronously. Be careful thought as it might not quite work as it appears too i.e. If you debug the ABAP program logic it will step over the FM onto the next line of code, not waiting for this function module to finish it processing. But this doesn't mean it has gone off to start the processing at this point as it has not!! It has simply created the background task ready for processing and will not actually be executed until a commit work is reached in the current logical unit of work.
So basically if you want it to go off and perform this background processing straight away you need to add a commit work after the call function… in background task command.
Just in case you are interested in the technical details when you make the call using the in background task addition SAP stores the FM name, destination and any parameters in tables ARFCSSTATE & ARFCSDATA for the current Logical unit of work. These entries can also been seen using tcode SE58. Please note this data is not available here after the task has finished processing.
Although this may seem strange at first it does allow you to perform other functionality first and only triggers the background task if all is well with that and it is committed to the database ok. Also the background tasks will be processed in the order they have been registered.
AS SEPARATE UNIT
The "as separate unit” addition is used if you are calling the same FM multiple times or FM's within the same function group. It basically ensures each call is processed within its own context and is not affected by global data changes from other function calls.
This simple allows you to specify a different RFC destination
Example ABAP code to Execute FM in background task
CALL FUNCTION 'Z_FMODULE' IN BACKGROUND TASK EXPORTING P_UNAME = sy-uname. *IN BACKGROUND TASK additional options CALL FUNCTION 'Z_FMODULE' IN BACKGROUND TASK AS SEPARATE UNIT DESTINATION 'NONE' EXPORTING P_UNAME = sy-uname. break-point. "does not wait and continues with next line of ABAP code Commit Work. "Background task is only triggered at this point. "loop at itab into wa_itab. "... "endloop.